Epoxy resin-based gel coat for surface finishing of components made of fibre-reinforced plastics

ABSTRACT

A composition for the manufacture of a gelcoat includes a main component and a curing component. The main component includes at least one epoxide resin selected from glycidyl ethers of bisphenol A, glycidyl ethers of bisphenol F, trimethylolpropane triglycidyl ethers, and mixtures thereof, and up to 5 wt.-% of at least one of a filler and a pigment based on a total weight of the main component. The curing component includes at least one cycloaliphatic amine. The main component or the curing component further includes at least one polytetrahydrofuran polyol. The gelcoat is transparent.

CROSS REFERENCE TO PRIOR APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/402,314, filed on Nov. 20, 2014, which is a U.S. National Phaseapplication under 35 U.S.C. § 371 of International Application No.PCT/DE2013/000272, filed on May 21, 2013 and which claims benefit toGerman Patent Application No. 10 2012 010 583.5, filed on May 21, 2012.The International Application was published in German on Nov. 28, 2013as WO 2013/174362 A1 under PCT Article 21(2).

FIELD

The present invention relates to compositions based on epoxy resins forthe production of gelcoats and the use of said gelcoats for the surfacetreatment of fiber reinforced plastics. The present invention alsorelates to processes for the production of the gelcoats, as well as toprocesses for the manufacture of surface treated components made offiber reinforced plastics, in particular to manufacturing processes thatemploy prepegs.

BACKGROUND

Surfaces of laminates or components composed of fibers such as glassfibers, carbon fibers, or plastic fibers in a matrix of curable resinssuch as epoxy resins, unsaturated polyester resins, or vinyl esterresins generally feature less acceptable surfaces, which, moreover, arenot resistant to light and weathering. These must first be treated withprotective coatings if these components are to be employed inapplications for which decorative or weather-resistant surfaces arerequired.

Components' surfaces are as a rule painted with suitable coatingmaterials, predominantly weather-resistant and anticorrosive paints, forexample, those based on aliphatic polyurethanes. To ensure sufficientadhesion of the coating to the component, the surfaces to be paintedmust, however, first undergo complex pretreatment. Surfaces ready forpainting are usually obtained following a number of process steps. Thesurface of the demolded component is first sanded to effect a completeremoval of any mold releasing agents. The surface is then coated orsmoothed with a filling compound to level out any surface defects suchas pores or individual protruding fibers exposed by the sandingtreatment. Once the filling compound has hardened, the surface is againsanded to obtain a smooth surface ready for painting.

One alternative to this time-consuming and laborious pretreatmentprocess is the application of a gelcoat. A gelcoat is a compositionbased on a resin system and is applied to the surfaces of componentsusing an in-mold composite construction process. The use of gelcoatsyields smooth surfaces during the manufacturing process of thecomponent, which surfaces are ideal for sanding. The surfaces may thenbe painted immediately following sanding. The gelcoat is generallyplaced in a component mold as the first layer, which is then pre-curedor incipiently gellated to an extent at which the dryness grade 6 inaccordance with DIN 53 150 has been reached, at which it complies withthe mechanical requirements for subsequent processing. Fibers, forexample, in the form of woven fabrics, non-woven fabrics, or laid webs,and the laminating resin containing the thermosetting resin employed asa matrix are then placed on the partially gellated gelcoat film. Theentire composition is then hardened to completion. The gelcoat film mustbe sufficiently stable that the fibers can be applied, and wherenecessary removed again, without damaging the film. In the case ofextremely large molds, such as rotor blades for wind turbines, wovenfabrics or non-woven fabrics are usually applied by hand. It mustconsequently also be possible to walk on the gelcoat film without thefilm sustaining damage.

Use has until now been made of filled gelcoats. The filler distributedin the resin system forms a framework which provides the requiredmechanical stability with only minimal precuring or only after minimalprogression of the curing reaction of the gelcoat. The use oftransparent gelcoats is more advantageous since laminating flaws, suchas gas bubbles or dry areas in the laminate which have not been coatedby resin, can be readily detected and repaired following removal of thecomponent from the mold. Transparent gelcoats not containing fillerrequire a much more intense curing process to0 achieve the requiredstability of the film. More intense progression of the curing reaction,however, results in considerably shorter laminating times. Thelaminating time is taken to be the amount of time occurring between thepoint in time at which the gelcoat placed in the mold becomes tack-freeand the point in time at which the gelcoat film must be sufficientlylaminated to provide adhesion between the gelcoat and the laminate.

For these reasons, transparent gelcoats are as yet only employed for theproduction of laminates using liquid laminating resins. In prepregprocedures, the mechanical stability of the gelcoat film must beconsiderably higher since the tackiness of the prepreg impedes handlingand, in particular, application thereof on the gelcoat film. It is notgenerally possible to adjust positioning since the film will tear uponremoval of the prepreg from the gelcoat film, or the entire compositionmight even be wrenched out of the mold. If the gelcoat film is subjectedto more intense curing to attain greater stability, however, thelaminating time will be insufficient for the formation of laminatelayers, particularly in relatively large molds.

SUMMARY

An aspect of the present invention is to provide improved materials andprocedures to allow for the use of transparent gelcoats, in particularin prepreg procedures, whilst retaining the known advantages thereof.

In an embodiment, the present invention provides a composition for themanufacture of a gelcoat which includes a main component and a curingcomponent. The main component comprises at least one epoxide resinselected from the group consisting of glycidyl ethers of bisphenol A,glycidyl ethers of bisphenol F, trimethylolpropane triglycidyl ethers,and mixtures thereof, and up to 5 wt.-% of at least one of a filler anda pigment based on a total weight of the main component. The curingcomponent comprises at least one cycloaliphatic amine. The maincomponent or the curing component further comprises at least onepolytetrahydrofuran polyol. The gelcoat is transparent.

DETAILED DESCRIPTION

The compositions of the present invention for the production of agelcoat contain a main component which contains at least one or moreepoxy resins, and a curing component which contains one or more amines.Unlike the conventional gelcoat resin systems based on radically curingresins, such as unsaturated polyesters (UP), vinyl esters, oracrylate-terminated oligomers, the epoxy resin-based gelcoats accordingto the present invention do not indicate any monomeric emissions. Theyalso show only minimal shrinkage during curing, or no shrinkage at all,and thus avoid stresses in the composite material or gelcoat boundarysurface so as to provide a stable boundary surface. Epoxy resin-basedcomposite materials (EP) moreover demonstrate excellent adhesion to thegelcoats of the present invention.

Epoxy resins suitable for use in the present invention are aromaticglycidyl compounds such as glycidyl ethers of bisphenol A, glycidylethers of bisphenol F, phenol novolak glycidyl ethers, cresol novolakglycidyl ethers, glyoxal tetraphenol tetraglycidyl ethers, p-tert.butylphenol glycidyl ethers, cresyl glycidyl ethers, N,N-diglycidylaniline, p-aminophenol triglycid, tetraglycid-4,4′-methylene dianiline,cycloaliphatic glycidyl compounds such as methyl tetra hydro phthalicdiglycidyl ether, hexahydrophthalic diglycidyl ether, cyclohexanedimethanol diglycidyl ether, glycidyl ethers of hydrated bisphenol A andglycidyl ethers of hydrated bisphenol F, epoxidated cycloolefins,aliphatic glycidyl ethers such as trimethylolpropane triglycidyl ether,the diglycidyl ethers of 1,6-hexane diol and 1,4-butane diol, n-dodecylglycidyl ether, n-tetradecyl glycidyl ether, as well as glycidyl ethersof polyoxyethylene polyols. Low-viscosity and medium-viscosity fluidepoxy resin types, semi-solid and solid epoxy resin types as well ascombinations thereof may also be used. In accordance with the presentinvention, the use of glycidyl ethers of bisphenol A, glycidyl ethers ofbisphenol F, trimethylol propane triglycidyl ethers and combinationsthereof can, for example, be used. Epoxy resins are used in quantitiesof from 40 to 90%, for example, between 60 and 80%, and, for example,between 65 and 75% by weight, based on the main component.

The composition furthermore contains one or more polyols. The polyolsmay be present in the main component as well as in the curing component.In accordance with the present invention, the polyols can, for example,be used in the main component. Suitable polyols include polyacrylatepolyols, polyester polyols, polyether polyols, polycarbonate polyols,polycaprolactones, and polyurethane polyols. The average molecularweights based on the number average of polyols can, for example, be 1000to 3000 g/mol, for example, between 1500 and 2500 g/mol, and, forexample, between 1800 and 2000 g/mol. The polyols are applied in amountsof from 2 to 40%, for example, between 5 and 30%, and, for example,between 10 and 20%, by weight of polyols, based on the main componentincluding the polyols. Polytetrahydrofuran polyols can, for example, beused.

In order to facilitate application of the transparent gelcoat, fillersand/or pigments may be added in small amounts. The fillers areconsidered below to be particulate substances virtually insoluble in theapplication medium and are used in order to influence the opticalcharacteristics. They may moreover also be conducive to increasingvolume in order to achieve or improve technical properties. The termpigments relates below to substances that are virtually insoluble in theapplication medium and that are applied as chromophoric substances ordyes. The compositions of the present invention are very slightly dulledwith fillers and/or pigments to facilitate management thereof to theeffect that material which has already been applied is more readilydiscernible during the application process. In this regard, the contentof fillers and/or pigments in the main component of the compositions ofthe present invention can, for example, be not more than 5%, forexample, not more than 2%, for example, not more than 1%, and, forexample, not more than 0.5%, by weight of the main component. Thecomposition will become non-transparent if greater quantities are added.Suitable fillers and pigments include mineral materials such as kaolinor talcum, synthetic materials such as barium sulphate or calciumcarbonate, and also inorganic or organic pigments as used conventionallyin paint production, and combinations thereof. Titanium dioxide or sootcan, for example, be used in accordance with the present invention.

In an embodiment of the present invention, the curing component can, forexample, contain one or more amines. Suitable amines include polyaminesselected from the group consisting of polyethylene polyamines such asethylene diamine, diethylene triamine, triethylene tetramine,tetraethylene pentamine, pentaethylene hexamine, pentane-1,3-diamine,2-methyl pentamethylene diamine, propylene amines such as propylenediamine, dipropylene triamine, dimethylaminopropylamine, trimethylhexamethylene diamine, polyether polyamines such as polyoxypropylenediamines or polyoxypropylene triamines, polyoxypropylene polyamines,polyoxyethylene polyamines, polytetrahydrofuran polyamines, orbutanediolether diamines or N-aminopropyl cyclohexyl amine, alkylenediamines such as hexamethylene diamine, trimethylhexamethylene diamine,or methyl pentamethylene diamine, cycloaliphatic amines such astricyclododecane diamine, N-aminoethyl piperazine, isophorone diamine,or diaminocyclohexane, aromatic amines such as diaminodiphenylmethane ordiaminodiphenylsulfone, araliphatic amines such as m-xylylene diamineand modifications thereof, for example, polyaminoamides, Mannich basesand epoxy adducts, as well as combinations thereof. Cycloaliphaticamines, and in particular isophorone diamine, can, for example, be used.The amines are added in quantities of from 60 to 100%, for example,between 80 and 95%, and, for example, between 85 and 95% by weight ofthe curing component.

The curing components of the present invention may additionally includeaccelerants. Suitable accelerants are tertiary amines such asN,N-dimethyl aniline or dimethyl benzylamine, alkoxides, imidazoles,Mannich bases such as (dimethyl aminomethyl)phenol or tris(dimethylaminomethyl)phenol, boron trifluoride complexes, Broensted acids, alkylphenols, polyphenols, onium salts, triarylsulfonium salts, iron arenecomplexes or salts of alkali metals or of alkaline earth metals such aslithium bromide or calcium nitrate. Accelerants can, for example,include phenols, polyphenols, alkali metal salts or alkaline earth metalsalts. Calcium nitrate tetrahydrate can, for example, be added. Theaccelerator is added in quantities of from 0.2 to 40%, for example, from0.5 to 20%, and, for example, from 1 to 10% by weight of the curingcomponent.

The composition contains plasticisers. Suitable plasticisers arepolyurethane prepolymers having blocked isocyanate groups. Theplasticisers can be present in the main component as well as in thecuring component. Isocyanate prepolymers blocked with substitutedphenols and/or pyrazoles can, for example, be added in the maincomponent as described in EP 0688803 A1, the disclosure of which isincorporated by reference herein.

Linear polymers having terminal isocyanate groups blocked withalkylphenol groups can, for example, be used. If the plasticisers areadded to the curing component, isocyanate prepolymers in which theisocyanate groups are blocked with secondary monoamines, as described inEP 0457089 A2, can, for example, be used. The disclosure of EP 0457089A2 is incorporated by reference herein.

The compositions according to the present invention may further containconventional additives as commonly used by the person skilled in theart. Rheology modifiers such as fumed silica, flow control agents ordefoamers, for example, may thus be used in the usual quantities.

In accordance with the present invention, the use of epoxy resins andamines can, for example, be used in the molar ratio of epoxy groups toN—H-groups reactive to epoxy groups (EP:N—H) of from 1 to 0.7 to 1 to1.4, for example, from 1 to 0.8 to 1 to 1.3, and, for example, from 1 to0.9 to 1 to 1.2.

The gelcoats which can be produced from the compositions according tothe present invention are transparent, that is to say, they exhibit apoor hiding power. The hiding power of the gelcoat according to thepresent invention is defined in DIN EN ISO 2814 on a checkered card. Thehiding power measured thereby can only be ascertained at a filmthickness of more than 1 mm. The film thickness of an applied gelcoat isconsiderably less and usually measures approx. 500 μm.

The gelcoats according to the present invention show relatively shortgellation times. Due to these short gellation times, the hold time forthe mold is reduced considerably, allowing for shorter mold hold cycles.The materials are tenacious and not brittle in the form of a gelcoatfilm in an insidiously gellated state. A comparison with regulartransparent gelcoats shows considerably superior elongation at break andtear propagation strength in the case of the gelcoat according to thepresent invention. Repositioning of applied prepregs according to thepresent invention without causing damage thereto is also possible whenusing the gelcoat films.

Despite their transparency, the gelcoats according to the presentinvention exhibit the mechanical stability required for subsequentprocessing stages. They in particular also fulfill the requirements forthe manufacture of laminates or fiber plastic composite components inthe prepreg process. As with the conventional, filled gelcoats, theyalso exhibit excellent adhesion to the laminate, are easily sanded in acured state, and are suitable for the application of paint thereon.

The present invention also provides the use of the gelcoat according tothe present invention for the surface treatment of fiber plasticcomposite components or laminates. The gelcoat can, for example, beapplied to surfaces of the component using the in-mold method. Thegelcoat film is placed in the component mold as a first layer to thisend. The composition according to the present invention is first addedto a mold following mixing of its reaction components, the maincomponent and the curing component, within the pot life. The pot life isthe period during which the mix remains workable. It begins at the pointin time at which the two reaction components are mixed and ends at thepoint in time at which the viscosity of the reaction mixture has risento such an extent that it is possible to apply a layer that is even inthickness. The layer obtained following gellation is sufficientlymechanically stable that it does not sustain damage upon application ofthe laminating resin and the fibers, but is sufficiently reactive tocreate a stable bond when the laminating resin cures. Examples of thelaminating resins used are epoxy resins, unsaturated polyester resins,and vinyl ester resins. Examples of the fibers used are woven fabrics,laid webs, and non-woven fabrics of glass, carbon, or plastic fibers. Toprovide sufficient adhesion between laminating resin and gelcoat, thegelcoat layer must be brought into contact with the laminating resinwithin the laminating period of the gelcoat. The laminating resin andgelcoat will then harden to completion.

The gelcoats according to the present invention can, for example, beused for the surface treatment of epoxy resin composite materialsbecause they exhibit better adhesion to these materials than gelcoatbased on other resinous systems. They also do not contain any volatilemonomers and are therefore less encumbering with regard to industrialhygiene.

The present invention also provides a method for manufacturingsurface-treated fiber plastic composite components or laminates.Firstly, the required two components, the main component and the curingcomponent, are mixed with the composition of the present invention. Themixture is transferred to the component mold as a first layer using theapplication method conventionally applied by the expert, for example, bypainting, rolling, spraying, or pouring. The applied mixture is thengellated or pre-cured to form a gelcoat film. Fibers in the form ofwoven fabrics, laid webs, or non-woven fabrics, as well as thelaminating resin are then applied to the gelcoat film. In the nextstage, the entire composite mixture is hardened to form the desiredcomponent. The component is then removed from the mold and its surfaceis subsequently sanded and then painted.

Fibers and laminating resins can be applied to the gelcoat film byvarious methods. Usual laminating methods, such as the vacuum bagmethod, the injection method, the infusion method, and the wetlaminating method are known to the person skilled in the art. One way ofproducing the fiber composite material involves the use of prepregs.Prepregs are impregnated resin/fiber mats which are placed in thecomponent mold. The resin is partially pre-cured and exhibits relativelystrong adhesion properties at room temperature. One problem incurred bythe use of prepregs is that of repositioning on the gelcoat film.Component molds are generally pretreated with a mold release agent toensure that the gelcoat film itself will not stick to the mold. Whenadhesive prepreg is applied to the gelcoat and then removed therefrom,the gelcoat should not tear or break. Since there is no adhesivenessrelatively to the mold, the gelcoat film must accordingly bemechanically stable. The gelcoats according to the present inventionform films which exhibit the required mechanical properties, and cantherefore be used in prepreg methods. The compositions of the presentinvention also require only short gellation times. Since the curingprocess is considerably quicker in the prepreg method than in othermethods, they are particularly suitable for use in these methods alsofor this reason.

Examples of gelcoat compositions according to the present invention areexamined below to compare the properties of the gelcoats according tothe present invention with those of commercially-used transparentgelcoats.

TABLE 1a Composition of Main Component Content in parts by weightSubstance S1 S2 S3 Bisphenol A diglycidyl ether 25 25 25 Bisphenol Fdiglycidyl ether 10 10 10 Trimethylol propane triglycidyl ether 40 47 40Polytetramethylene oxide polyol 12 — — Polypropylene oxide polyol — 1512 Plasticiser 10 — 10 Fumed silica 2.99 3 2.99 Titanium oxide 0.01 —0.01

TABLE 1b Composition of Curing Component Content in parts by weightSubstance HA HB Isophorone diamine 65 92 Phenolic accelerator 35 —Calcium nitrate tetrahydrate — 4 Propandiol — 4

TABLE 1c Composition of Gelcoat Main Curing Molar proportion Example No.component component MP 1.1 S1 HB 1.09 1.2 S1 HA 1.13 1.3 S2 HB 0.87 1.4S3 HA 1.07 2.1 Commercially available transparent gelcoat 2.2Commercially available transparent gelcoat

The following tests for elongation at break properties, tear propagationresistance, and prepreg re-position ability were performed on gelcoatfilms gellated under various curing conditions.

The elongation at break was determined via a mandrel bending test inaccordance with the test specification set forth in DIN EN ISO 1519.Metal plates, to which the coating under test were applied, were bentaround a mandrel. The smaller the radius of the mandrel around which theplate could be bent without damaging or fracturing the coating, thegreater the elongation at break of the coating.

The tear propagation resistance was determined via tear propagationtests in accordance with test specification set forth in DIN EN ISO13937-2. The force necessary to enlarge a crack in the coatingundergoing examination was measured. The greater the applied force, themore tear-resistant the coating.

The prepreg repositioning was determined via the following test set-upwhich simulates a laminate structure in a component mold. A mold releaseagent was applied to a sufficiently large metal plate. A gelcoatcomposition was then coated over an area of 1 m² on the prepared plate.The composition was gellated on the gelcoat film at the prescribedtemperature and for the prescribed duration. A prepreg of dimensions DINA4 was laid centrally on the gelcoat film and pressed down firmly with adefined force for 1 minute. The prepreg was then removed swiftly at anangle of 90 °. Visible damage to the gelcoat film was rated as follows:

++ No changes + Detachment of the gelcoat film from the metal plate atup to three positions without damaging the gelcoat film itself 0Detachment at up to 10 positions with damage at a maximum of threepositions − Increased damage of the gelcoat film −− Total detachment ofthe gelcoat film from the metal plate

Tables 2a and 2b show the results of the tests on gelcoat films gellatedunder various conditions. The gelcoats according to the presentinvention show considerably improved values in relation to elongation atbreak and tear growth resistance. In contrast to commercially availablegelcoats, the removal of a prepreg applied under pressure did not causeany damage to the gelcoat according to the present invention. It maythus be applied in processes involving prepregs without incurring theusual disadvantages.

TABLE 2a Properties of the gelcoat film gellated at 60° C. (Temperaturewas maintained until a dryness grade of 6 according to DIN 53 150 wasreached.) Gelcoat no. 1.1 1.2 1.3 1.4 2.1 2.2 Elongation at breakMandrel diameter in [mm] 40 25 8 12 1) 1) without fracture Mandreldiameter in [mm] 25 20 6 8 220 220 with fracture Tear growth resistanceForce in [N/mm] 3.7 1.1 0.5 2.8 2) 2) Prepreg repositioning abilityDamage assessment ++ ++ + ++ −− −− 1) Value was not determined 2) Valuenot measurable due to splintering of the coating

TABLE 2b Properties of the Gelcoat Film Gellated at 23° C. (Temperaturewas maintained for 18 hours.) Gelcoat no. 1.1 1.2. 1.3 1.4 2.1 2.2Elongation at break Mandrel diameter in [mm] 40 55 40 25 1) 1) withoutfracture Mandrel diameter in [mm] 32 40 32 32 220 220 with fracture Teargrowth resistance Force in [N/mm] 4.3 4.5 0.3 2.1 2) 2) Prepregrepositioning ability Damage assessment ++ ++ + ++ −− −− 1) Value wasnot determined 2) Value not measurable due to splintering of the coating

The following tests for adhesion of the laminate to the gelcoat, forsandability, and for paintability were performed on the cured laminates.The gelcoat compositions were placed in a mold and gellated, the prepregwas then applied to the gelcoat film. The mold was sealed and a vacuumbag attached and evacuated. The entire composition was then cured, thecuring conditions being prescribed by the respective prepreg used. Thefollowing tests were performed on the cured laminates.

The elongation at break was determined using the aforementioned mandrelbending test. Metal strips were coated in gelcoat as described above,the gelcoat being gellated and cured under the same temperatureconditions as those applied for curing of the prepreg laminates. Thesmaller the mandrel diameter, the greater the elongation at break. Theadhesive strength of the gelcoat on the laminate was determined by meansof pull-off tests in accordance with test specification set forth in DINEN ISO 4624. The greater the force required to pull off the seal, thestronger the adhesion.

In order to assess the laminate surfaces treated with gelcoat, theirsandability, i.e., their abrasion resistance, and their paintability,i.e., the adhesion of paint coats on their surfaces, were determined.The resistance to abrasion was determined gravimetrically in accordancewith test specification set forth in ASTM D 4060 using a S33 wheelrotating at 500 rpm under a load of 1000 g. The greater the differencein weight, the higher the abrasion resistance and, consequently, thebetter the sandability.

For the purpose of assessing the paintability, the laminate surfaceswere first sanded with grade 180 sandpaper. The sanding dust was thenremoved from the surface, which was then painted with a suitablecommercially available paint. On completion of curing of the paint film,the adhesion thereof, i.e., its adhesive strength, was determined bymeans of stripping tests in accordance with test specification set forthin DIN EN ISO 4624. The greater the tension required to pull off thefilm, the stronger the adhesion.

Table 3 shows the results on the surface-treated laminate according tothe present invention compared with regular surface-treated laminates.The laminates according to the present invention also fulfill, as in thecase of the regular laminates, all requirements with regard to adhesion,sandability, and paintability.

TABLE 3 Properties of the Cured Laminates Gelcoat no. 1.1 1.2. 1.3 1.42.1 2.2 Elongation at break Mandrel diameter in [mm] 70 70 85 70 70 85with no fracture Mandrel diameter in [mm] 55 55 70 55 55 70 withfracture Adhesion of gelcoat to laminate Stripping tension in [N/mm²]9.1 9.8 8.7 9.2 8.9 8.8 Taber abrasion Difference in [mg] 986 864 793891 762 1) Adhesion paint on gelcoat Stripping tension in [N/mm²] 6.35.3 6.1 5.9 6.6 4.4 1) Not determined

The present invention is not limited to embodiments described herein;reference should be had to the appended claims.

What is claimed is:
 1. A composition for the manufacture of a gelcoat,the composition comprising: a main component comprising, at least oneepoxide resin selected from the group consisting of glycidyl ethers ofbisphenol A, glycidyl ethers of bisphenol F, trimethylolpropanetriglycidyl ethers, and mixtures thereof, and up to 5 wt.-% of at leastone of a filler and a pigment based on a total weight of the maincomponent; and a curing component comprising at least one cycloaliphaticamine, wherein, the main component or the curing component furthercomprises at least one polytetrahydrofuran polyol, and the gelcoat istransparent.
 2. The composition as recited in claim 1, wherein the maincomponent comprises up to 2 wt.-% of the at least one of a fillers and apigment based on the total weight of the main component.
 3. Thecomposition as recited in claim 1, wherein the at least one epoxideresin of the main component is present in an amount of from 40 to 90wt.-% based on the total weight of the main component.
 4. Thecomposition as recited in claim 1, wherein the main component comprisesthe at least one polytetrahydrofuran polyol in an amount of from 2 to 40wt.-% based on the total weight of the main component.
 5. Thecomposition as recited in claim 4, wherein the at least onepolytetrahydrofuran polyol has an average molecular mass of from 1000 to3000 g/mol based on a number average molecular weight.
 6. Thecomposition as recited in claim 1, wherein the at least onecycloaliphatic amine of the curing component is present in an amount offrom 60 to 100 wt. % based on a total weight of the curing component. 7.The composition as recited in claim 1, wherein the at least onecycloaliphatic amine is isophorone diamine.
 8. The composition asrecited in claim 1, wherein the at least one epoxide resin comprisesepoxide groups and the at least one cycloaliphatic amine comprises N—Hgroups, the epoxide groups and the N—H groups being present in a molarratio of from 1 to 0.7 to 1 to 1.4.
 9. The composition as recited inclaim 1, wherein the composition further comprises at least oneplasticizer selected from the group consisting of polyurethaneprepolymers having blocked isocyanate groups.
 10. The composition asrecited in claim 1, wherein the main component further comprises atleast one plasticizer consisting of isocyanate prepolymers blocked withat least one of substituted phenols and pyrazoles.
 11. The compositionas recited in claim 1, wherein the curing component further comprises atleast one plasticizer consisting of isocyanate prepolymers blocked withsecondary monoamines.
 12. A method of using a gelcoat for a surfacetreatment of a fiber reinforced compound plastics material, the methodcomprising: providing a fiber reinforced compound plastics material;providing the composition as recited in claim 1; manufacturing thegelcoat from the composition; and surface treating the fiber reinforcedcompound plastics material with the gelcoat.
 13. A method formanufacturing a surface-treated fiber-reinforced compound plasticsmaterial as a construction element, the process comprising: providingthe composition as recited in claim 1; mixing the main component and thecuring component of the composition so as to obtain a mixture; placingthe mixture in a component mold; allowing the mixture to gel so as toform a gelcoat film; applying a woven fabric, a non-woven fabric, or alaid fabric together with a laminating resin to the gelcoat film so asto obtain a laminate; and curing the laminate so as to form theconstruction element.
 14. The method as recited in claim 13, furthercomprising: providing the woven fabric, the non-woven fabric, or thelaid fabric together with the laminating resin as at least one prepreg;and applying the at least one prepreg on the gelcoat film so as toobtain the laminate.
 15. The method as recited in claim 13, wherein themixture is placed in the component mold and the mixture allowed to gelso as to form a gelcoat film in a non-covering thickness.
 16. Astructural element of a fiber-reinforced compound plastics material,wherein a surface of the structural element is coated with the gelcoatlayer produced from the composition as recited in claim
 1. 17. Thestructural element as recited in claim 16, wherein the structuralelement is a rotor blade for a wind turbine.